Weak-link Network Research Articles

From the periphery to the centre: a bibliometric review of global virtual teams as a new ordinary workplace

PurposeThis study aims to offer a bibliometric analysis of the already substantial and growing literature on global virtual teams (GVTs).Design/methodology/approachUsing a systematic literature review approach, it identifies all articles in the Web of Science from 1999 to 2021 that include the term GVTs (in the title, the abstract or keywords) and finds 175 articles. The VOSviewer software was applied to analyze the bibliometric data.FindingsThe analysis revealed three dialogizing research clusters in the GVTs literature: a pioneering management information systems and organizational cluster, a general management cluster and a growing international management and behavioural studies cluster. Furthermore, it highlights the most cited articles, authors, journals and nations, and the network of strong and weak links regarding co-authorships and co-citations. Additionally, this study shows a change in research patterns regarding topics, journals and disciplinary approaches from 1999 to 2021. Finally, the analysis illustrates the position and centrality in the network of the most relevant actors.Practical implicationsThe findings can guide management practitioners, educators and researchers to the most meaningful clusters of publications on GVTs, and help navigate and make sense of the vast body of the available literature. The importance of GVTs has been growing in the past two decades, and Covid-19 has accelerated the trend.Originality/valueThis study provides an updated and comprehensive systematic literature review on GVTs. To the best of the authors’ knowledge, it is also the first systematic literature review and bibliometry on GVTs. It concludes by suggesting future research paths.

Influence of ionomer adsorption on agglomerate structures in high-solid catalyst inks

Because the agglomerate structures of carbon-black-supported platinum nanoparticles (Pt/C) in catalyst inks affect their productivity and performance, identifying the structural parameters that control the dispersion state and stability of Pt/C agglomerates is important. This study aimed to identify agglomerate structures of Pt/C in high-solidity catalyst inks by examining the rheological behavior, fractal dimension, and electrical conductivity of the inks. In inks containing 48–75% water, the amount of adsorbed ionomers decreased with decreasing water content, resulting in increases in the shear viscosity (η), storage modulus (G′), and electrical conductivity (Σ). The fractal dimension of the agglomerates (df) was 1.7–2.1, suggesting that Pt/C agglomerates form a rigid three-dimensional network via a diffusion-limited cluster aggregation process. Conversely, in inks containing 89% water, the amount of adsorbed ionomers increased, leading to the lowest values for η, G′, and Σ. The df value was 2.6, suggesting that Pt/C agglomerates formed a weak-link network via a reaction-limited cluster aggregation process, which was inhibited by the steric and electrostatic repulsion effects of the adsorbed ionomers. The results of this study demonstrate that agglomeration can be controlled through ionomer adsorption by Pt/C, leading to changes in the rheological behavior and stability of catalyst inks.

Manipulation of Recrystallization and Network Formation of Oil-Dispersed Micronized Fat Crystals.

A detailed investigation was carried out on the modulation of the coupling between network formation and the recrystallization of oil-dispersed micronized fat crystal (MFC) nanoplatelets by varying oil composition, shear, and temperature. Sunflower (SF) and bean (BO) oils were used as dispersing media for MFC nanoplatelets. During MFC dispersion production at high shear, a significant increase in the average crystal thickness (ACT) could be observed, pointing to recrystallization of the MFC nanoplatelets. More rapid recrystallization of MFC occurred in the SF dispersion than in the BO dispersion, which is attributed to higher solubility of MFC in the SF oil. When the dispersions were maintained under low shear in narrow gap Couette geometry, we witnessed two stages of recrystallization (measured via rheo-SAXD) and the development of a local yield stress (measured via rheo-MRI). In the first stage, shear-enabled mass transfer induces rapid recrystallization of randomly distributed MFC nanoplatelets, which is reflected in a rapid increase in ACT (rheo-SAXD). The formation of a space-filling weak-link MFC network explains the increase in yield stress (assessed in real time by rheo-MRI). In this second stage, recrystallization slows down and yield stress decreases as a result of the formation of MFC aggregates in the weak link network, as observed by confocal Raman imaging. The high fractal dimension of the weak-link network indicates that aggregation takes place via a particle-cluster mechanism. The effects of oil type and shear on the recrystallization rate and network strength could be reproduced in a stirred bowl with a heterogeneous shear stress field, which opens perspectives for the rational manipulation of MFC thickness and network strength under industrial processing conditions.

The topology of overlapping portfolio networks

Abstract This paper analyzes the topology of the network of common asset holdings, where nodes represent managed portfolios and edge weights capture the impact of liquidations. Asset holdings data is extracted from the 13F filings. We consider the degree centrality as the degree in the subnetwork of weak links, where weak links are those that lead to significant liquidations. We explore the applications of this network representation to clustering and forecasting. To validate the weight attribution and the threshold used to define the weak links, we show that the degree centrality is correlated with excess returns, and is significant after we control for the Carhart four factors. The network of weak links has a scale free structure, similar to financial networks of balance sheet exposures. Moreover, a small number of clusters, densely linked, concentrate a significant proportion of the portfolios.

The Topology of Overlapping Portfolio Networks

This paper analyzes the topology of the network of common asset holdings, where nodes represent managed portfolios and edge weights capture the impact of liquidations. We consider the degree centrality as the degree in the subnetwork of weak links, where weak links are those that lead to significant liquidations. We explore the applications of this network representation to clustering and forecasting. To validate the weight attribution and the threshold used to define the weak links, we show that the degree centrality is correlated with excess returns, and is significant after we control for the Carhart four factors. The network of weak links has a scale free structure, similar to financial networks of balance sheet exposures. Moreover, a small number of clusters, densely linked, concentrate a significant proportion of the portfolios.

Connectivity and critical current density of in-situ processed MgB2 superconductors: Effect of excess Mg and non-carbon based additives

In a sequel to our previous paper (J. Appl. Phys. 113, 036908 (2013)), where we reported comprehensive analysis of inter-grain connectivity (AF), pinning, percolation threshold (Pc), and anisotropy (γ) in a series of ex-situ processed MgB2, we address the same issues in in-situ processed samples. MgB2 samples with stoichiometric composition, excess Mg (5 wt. %) and further 3 wt. % addition of various non-carbon based additives like nano-Ag, nano-Ni, and YBCO are synthesised by the in-situ route. Detailed investigations of X-ray diffraction, magnetization (M), and resistivity (ρ) as a function of temperature (T) and field (B) in the range 5–300 K and 0–8 T are carried out in all the samples. The resistive superconducting onset Tcon ∼ 38.6 ± 0.3 K and offset (where ρ goes to zero) Tc0 ∼ 38.1 ± 0.3 K of the samples stay nearly unchanged. The inter-grain connectivity (AF) of the samples varies between 11%–20%. All the additives result in a critical current density (Jc) higher than the stoichiometric MgB2 sample, where the highest values (e.g., Jc(1 T, 5 K) ∼ 1.2 × 109 A/m2) are observed for the sample with 5 wt. % excess Mg. The major findings based on quantitative analysis of ρ (T, B) and Jc (B, T) data in all the samples are: (1) along with previously studied ex-situ samples, the Jc(AF) shows a significant increase at AF ∼ 7%; (2) the irreversibility lines lie lower than the characteristic Tc0(B) lines in the B-T phase diagram; (3) a universal core pinning (δl- and/or δTc- type) mechanism is revealed in the entire T range 5–30 K; and (4) typical values of Pc ∼ 0.57 ± 0.04 is indicative of weak link networks.

Enhancement of Flux Pinning in YBa2Cu3O7−δ + Ag Nanocomposites

YBa2Cu3O7−δ/Ag thin film is prepared through pulsed laser deposition. The presence of Ag brings about significant inter- and intragranular modification in the mi- crostructure of the composites. The resistive broadening in the tail part is suggested to be associated with the link be- tween the grains and to be extremely sensitive to magnetic fields. It is assumed that the zero resistance state at the Tc0 region of the above high temperature superconductor is gov- erned by the excitations in the weak link network. Invoking Beans critical state model, enhancement in critical current density Jc is observed.

Magnetic field dependence of the pinning effect in [formula omitted]-doped [formula omitted] ceramic superconductor

Y Ba 2Cu 3O 7−δ(Y BCO)+BaZrO 3 composites were prepared through the solid-state route, employing nitrate precursors of BaZrO 3 (BZO), yielding submicron particles. Invoking Bean’s critical state model, an enhancement of J c in composite samples in the presence of a magnetic field at a temperature ( T ) of 40 K has been observed. The resistive broadening in the tail part is suggested to be associated with the link between the grains and to be extremely sensitive to the magnetic field. It is assumed that the global zero-resistance state in the T c 0 region of high-temperature superconductivity (HTSC) is governed by the excitations in the weak-link network.

Description of the transport critical current density behavior of polycrystalline superconductors as a function of the applied magnetic field

Abstract A model to describe the critical current density behavior of high- T c polycrystalline superconductors is proposed for all magnetic field values. The main features of the model are as follows: the transport critical current density is controlled by the weak-link network at grain boundaries. The size distribution of weak links is well represented by a Gamma-type distribution. Finally, the tunneling critical current between grains follows a Fraunhofer diffraction pattern or a modified pattern if the applied magnetic field is lower or higher than the first critical field H c 1 .

Current–voltage characteristics of break junctions of high-Tc superconductors

The current–voltage (I–V) characteristics of break junctions of polycrystalline La1.85Sr0.15CuO4, Y0.75Lu0.25Ba2Cu3O7−δ, Bi1.8Pb0.3Sr1.9Ca2Cu3Ox and composite YBa2Cu3O7−δ+Ag are investigated. The experimental I–V curves exhibit the specific peculiarities of superconductor/normal-metal/superconductor junctions. The relation between an I–V characteristic of network of weak links and I–V dependencies of typical weak links is suggested to describe the experimental data. The I–V curves of typical weak links are calculated by the Kümmel–Gunsenheimer–Nicolsky model considering the multiple Andreev reflections.

Angular effects of the critical current inNb∕Pdmultilayers

in these structures. The results areexplained in terms of the magnetic field suppression of the percolation currents in a weak-link network. Fluxtrapped within grains by the flux pinning processes is relatively stable at low fields and its contributions to thetransport current suppression add vectorially to the applied field.DOI: 10.1103/PhysRevB.74.064509 PACS number s : 74.25.Qt, 74.78.Fk

Critical current of theSr2RuO4−Sr3Ru2O7eutectic system

We report critical current measurements of the ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}\text{\ensuremath{-}}{\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ eutectic system, a solid mixture of the spin-triplet superconductor ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and the nearly ferromagnetic metal ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$. Our results reveal that this eutectic forms an unusual superconducting state with features distinct from those of the pure ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ phase. We observe a crossover from Ambegaokar-Baratoff to Ginzburg-Landau type behavior in the temperature dependence of the critical current, similar to the behavior of Josephson weak-link networks in granular high-${T}_{c}$ cuprates. Our results suggest that large regions of ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ in this solid mixture may become superconducting by an unusual proximity effect.

Lower critical fields of a Y-Ba-Cu-O superconductor

The low-field properties of a Y-Ba-Cu-O superconductor are studied experimentally. A number of critical fields for the subsequent penetration of hypervortices and Josephson vortices into a weak-link network of superconducting ceramics are found.

Crossover from the “clean” limit to the “dirty” limit in a network of S-N-S weak links in Y3/4Lu1/4Ba2Cu3O7 + BaPb1−x SnxO3 (0≤x≤0.25) composites

Composites with a network of “superconductor-normal metal-superconductor” (S-N-S) weak links are prepared from a Y3/4Lu1/4Ba2Cu3O7 high-temperature superconductor and BaPb1−x SnxO3 (0≤x≤0.25) metal oxides. It is found that an increase in the tin content x in the nonsuperconducting component of the composite leads to an increase in the electrical resistivity ρ and, hence, to a decrease in the mean free path l of charge carriers. The temperature dependences of the electrical resistivity ρ(T) and critical current j C (T) of the composites are analyzed in the framework of the de Gennes theory of S-N-S junctions. It is demonstrated that the network of weak links in the composites is characterized by a crossover from the “clean” limit (l≥L) to the “dirty” limit (l≤L) (where L is the effective thickness of N interlayers between high-temperature superconductor grains).

Magneto-optical and electromagnetic studies of core connectivity and weak-link behaviour inCu/MgB2 and Ni/MgB2 wires and tapes

Critical current density, ac susceptibility (real part ) and magneto-optical (MO) imaging were used to characterize round wire and tapes made from pre-reactedMgB2 powder by the powder-in-tube method. Magnetic susceptibility measurementsindicated the existence of large-scale weak-link networks in the cores of as-deformedNi/MgB2 and Cu/MgB2 wires and tapes. As-deformed samples showed a two-step transition in versus T traces as evidence of weak links in the tape core. The first heat treatment (HT) ofas-deformed tapes led to a sharp susceptibility transition, very strong connection in thetape core as seen in MO images, and high critical current. A second rolling of anas-sintered tape induced a network of defects in the brittle core and gave rise to curve broadening, but did not result in a two-step transition. These data show thatdeformation-induced cracks are not the primary source of weak-link behaviour. A largedecrease in transport current was also registered in this sample. The second HT, for 30 min,restored the sharp magnetic transition and high transport current. Alternating areas ofstrong and weak connection in the tape core have been observed on MO images. Fastheating and cooling of the as-deformed tape with no dwell time at the maximumtemperature resulted in a strongly linked core with a sharp transition and increasedtransport current. After fast HT, no mechanical defects were observed in MO images. Suchfast transformation could be explained by rapid sintering due to highly strainedMgB2 grains.

Numerical analysis of the inhomogeneous current transport properties ofAg/Bi2Sr2Ca2Cu3O10tapes

The numerical analysis based on the two-dimensional weak link network model is carried out to investigate the influence of the microscopic inhomogeneities on $I\ensuremath{-}V$ characteristics of the Ag/Bi2223 tapes. The dependence of $I\ensuremath{-}V$ curves on the various parameters of the model (system size, effective coordination number, volume fraction, and connectivity) is calculated and statistical matters are discussed. It is revealed that the lattices having larger coordination number Z show better properties and volume fraction of superconducting (SC) phase is very important to have finite (nonzero) ${I}_{\mathrm{c}}.$ This indicates that it is very effective for improving the properties of the tapes to fabricate the tapes consisting of large Z grains and having high volume fraction of SC phase.

Superconducting properties of MgB2 thin films prepared on flexible plastic substrates

Superconducting MgB2 thin films were prepared on 50-μm-thick, flexible polyamide Kapton-E foils by vacuum co-deposition of Mg and B precursors with nominal thickness of about 100 nm and a subsequent ex situ rapid annealing process in an Ar or vacuum atmosphere. In the optimal annealing process, the Mg–B films were heated to approximately 600 °C, but, at the same time, the backside of the structures was attached to a water-cooled radiator to avoid overheating of the plastic substrate. The resulting MgB2 films were amorphous with the onset of the superconducting transition at Tc,on≈29 K and a transition width of approximately 3 K. The critical current density was >7×105 A/cm2 at 4.2 K, and its temperature dependence indicated a granular film composition with a network of intergranular weak links. The films could be deposited on large-area foils (up to 400 cm2) and, after processing, cut into any shape (e.g., strips) with scissors, or bent multiple times, without any observed degradation of their superconducting properties.

AC susceptibility of high Tc superconductor Tl 0.8Pb 0.2Bi 0.2Sr 1.6Ba 0.4Ca 2Cu 3O x using a critical state model

The Anderson–Kim model is employed to calculate the temperature and AC magnetic field dependence of the complex susceptibility, χ= χ ′+i χ ′′, of high T c superconductor Tl 0.8Pb 0.2Bi 0.2Sr 1.6Ba 0.4Ca 2Cu 3O x . Intergranular Josephson vortices sweep in and out of the weak-link network, while intragranular Abrikosov vortices move in and out of the superconducting grains, both causing bulk pinning hysteresis loss. The calculated χ ′ and χ ′′ are consistent with experimental data very well by considering the proper volume fraction of superconducting grains and intergranular region. Using field dependence of critical current density obtained from fitting parameter, the property of intergranular region is discussed and the intergranular lower critical field H c1J is determined.

Transport properties of HTSC + Ba(Pb, Met)O3 composites as functions of the electrical and magnetic characteristics of nonsuperconducting components

Composites simulating a network of weak metallic links and consisting of a classic 1–2–3 HTSC and a BaPbO3 metal oxide with incorporated Sn, Ni, and Fe impurities have been prepared. Experimental resistivity, magnetic, and Mossbauer studies of the BaPb0.9Met0.1O3 nonsuperconducting components are presented. The transport properties of the HTSC + BaPb0.9Met0.1O3 composites have been investigated. The superconducting properties of the composites are observed to be suppressed, both when the carrier mean free path in nonsuperconducting components with tin impurities decreases, and as a result of an additional interaction of the magnetic moments of (Fe, Ni) impurities with the spins of supercurrent carriers. The experimental temperature dependences of the composite critical current are analyzed in terms of the de Gennes theory for the superconductor-normal metal-superconductor structures.

Communication and Coordination in Social Networks

I model people in a coordination game who use a communication network to tell each other their willingness to participate. The minimal sufficient networks for coordination can be interpreted as placing people into a hierarchy of social roles or stages: initial adopters, then followers, and so on down to late adopters. A communication network helps coordination in exactly two ways: by informing each stage about earlier stages, and by creating common knowledge within each stage. We then consider two examples: first we show that dimensional networks can be better for coordination even though they have far fewer links than dimensional networks; second we show that wide dispersion of insurgents, people predisposed toward participation, can be good for coordination but too much dispersion can be bad. Although collective action depends on both social structure and individual incentives, these integral aspects have been formalized separately, in the fields of social network theory and game theory. By considering them together, this paper engages the classic question of which structures are conducive to coordination and shows that structure and strategy are related in a mutually interesting way. Here we consider a coordination game in which each person wants to participate only if others participate. Social structure is thought of as a communication network by which people tell each other their willingness to participate. Each person knows whether her neighbours in the network are willing, but does not know about anyone else. Our model is thus a game of incomplete information in which each person, given his local knowledge, decides whether to participate. The main result is a characterization of the minimal sufficient networks for coordination in terms of a hierarchy of social roles or stages: initial adopters, then followers, and so on down to late adopters, for example. A communication network helps coordination in exactly two ways: by informing each stage about earlier stages, and by creating common knowledge within each stage. We also consider two simple examples: first, we show that low dimension or strong link networks can be better for coordination even though they have far fewer links than high dimension or weak link networks; second, we show that wide dispersion of insurgents, people predisposed toward participation, can be good for coordination but too much dispersion can be bad. This paper is built on the assumption that the most basic and common mechanism for coordination is the I'll if you go mechanism: individuals first communicate with each other about their preferences, and then each individual chooses whether to participate or not. Hence a person's participation depends on what he knows about his neighbours; it does not depend solely on their participation itself, either through learning, adaptation, or social influence. The physical analogies of contagion or diffusion are not